The Sigtronics RES-401 is an aviation stereo retrofit music switcher designed to upgrade existing Sigtronics SPA-400 intercom installations with full stereo capability and crew/passenger audio management.

It allows integration of external stereo audio sources (such as radios, music players, or avionics audio outputs) into the aircraft intercom system without replacing the existing intercom unit. The system also provides crew isolate and automatic audio muting when radio transmissions or intercom activity occur.

Key features include:

Stereo retrofit module for SPA-400 intercom systems
Adds full stereo music capability and crew isolate function
Compatible with external audio sources (line or headphone level)
Automatic music muting during COM transmission or intercom use
Remote-mounted compact chassis design
Designed for aircraft panel retrofit installations
Supports pilot/passenger audio distribution modes
Compatible with SPA-400 / SPA-600 ecosystem (system dependent)
FAA/TSO environment compliant design (intercom system dependent)
Used in certified general aviation audio system upgrades